A second major effort involves the development and characterization of mouse models based on immune recognition of tumor cells endogenously expressing tumor-associated (TAA) or tumor-specific Ag (TSA). The purpose here will allow us to translate at least some of the concepts or observations made from in vitro human studies to in vivo settings of animal models reflecting antigenically relevant tumor rejection epitopes. We have developed a CTL-p53 TAA model, based on immune recognition of a WT p53 determinant. WT p53 peptide-specific, MHC class I-restricted CTL were produced from immune competent C57BL/6 (H-2b) mice after immunization with a previously defined WT p53 peptide (p53232-240). Epitope-specific CTL were then employed to identify syngeneic tumor cell populations expressing that antigenic determinant. Two tumor cell lines, MC38 colon carcinoma and MC57G fibrosarcoma, were demonstrated to naturally express the endogenous WT p53232-240 determinant as defined by CD8+ CTL recognition. We demonstrated that the adoptive transfer of WT p53-specific CTL to mice with 3-day established pulmonary metastasis of MC38 cells resulted in antitumor activity in vivo. The CMS4 tumor cell line is a chemically induced sarcoma established from BALB/c (H-2d) mice. Tumor-specific CD8+ CTL were produced in vivo, which recognized an H-2Ld-restricted nonamer epitope peptide derived from an envelop protein (gp70) of an endogenous murine leukemia retrovirus. This was based upon CTL cross-reactivity against syngeneic CT26 colon carcinoma cells previously characterized to express that gene product, as well as by cold target inhibition assays. The adoptive transfer of CMS4-reactive CTL in vivo resulted in potent antitumor activity against both 3-day and 10-day established pulmonary metastases. Our data also indicated that treatment of CMS4 cells with IFN-gamma plus TNF-alpha rendered them sensitive to Fas-mediated lysis ensuing engagement with agonistic anti-Fas mAb. Thus, the objectives of future studies include: (1) to examine the potential role of Fas/FasL interactions in the regulation of antitumor CD8+ CTL responses in vivo; and (2) to produce, characterize and explore antitumor properties of Ag-specific CD8+ CTL subtypes in vitro and in vivo.